When using the Highway Emergency Flasher you'll be clearly visible from well over a mile away. This flasher is water resistant and measures over six inches long and four inches wide. It uses eighteen super bright LEDS which can be either remain on or flash in order to warn or signal approaching cars. To attach it securely to the back of a car, truck, bicycle, or any metal object there are two rare earth magnets on the back of the unit. This new type of magnet is smaller and far superior in strength to regular magnets. Also includes a built-in stand. Requires four 'AA' batteries.